Inactivation of hepatitis A virus in heat-treated mussels

Control of Viral Contamination of Food and Environment

Viruses are often transmitted via food and the environment. Contamination may be controlled either by preventing its occurrence or by inactivating the contaminating virus. The majority of agents transmitted in this way are human enteric viruses, produced either in the intestines or the liver. They are shed in human feces (noroviruses also in vomitus) in a broad range of circumstances, and they are relatively stable outside the host. Non-enteric viruses are less often transmitted via foods and are generally less environmentally stable. Insofar as vaccines are available, they are able to prevent fecal shedding. Viruses shed in feces via the water-carriage toilet may be eliminated by proper treatment and disinfection of the wastewater. In the foods context, the most effective antiviral measures are cooking and hand washing. Detection methods are most useful after the fact, in investigating outbreaks and devising preventive measures.

Evaluation of two viral extraction methods for the detection of human noroviruses in shellfish with conventional and real-time reverse transcriptase PCR

AIMS

Comparison of two viral extraction methods in order to establish a sensitive and simple detection method for human noroviruses (NV) in bivalve shellfish.

METHODS AND RESULTS

A direct RNA extraction method and an alkaline virus elution-concentration method were tested on artificially contaminated mussels. The latter used an alkaline buffer and polyethylene glycol (PEG) to isolate and concentrate the virus particles from shellfish. In both methods Trizol was used to release RNA. The final RNA extracts were amplified and detected with conventional and real-time reverse transcriptase PCR. The direct RNA extraction method was not able to detect low inoculation levels. However, the virus elution-concentration method was more sensitive.

CONCLUSIONS

The alkaline elution-PEG concentration method followed by Trizol effectively removed inhibitory components and fulfilled the demands to be a useful tool for routine testing of shellfish for NV detection.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because of the lack of standardized methods to detect NV in shellfish, many 'in-house' extraction methods are used in practice. A comparison of these methods aims to determine a simple, rapid and sensitive method that could be a candidate method for screening suspected shellfish.

Effect of heat treatment on hepatitis A virus and norovirus in New Zealand greenshell mussels (Perna canaliculus) by quantitative real-time reverse transcription PCR and cell culture

Quantitative real-time reverse transcription PCR (qRT-PCR) and cell culture (50% tissue culture infectious dose [TCID50]) were used to determine the effect of heat treatments on norovirus and hepatitis A virus (HAV) in the New Zealand Greenshell mussel (Perna canaliculus). Since it is common practice to cook mussels until the shells open, internal temperatures and opening times of mussels on boiling and steaming were determined at regular time intervals. Fifty mussels in batches of six were exposed to boiling and steaming. A mean internal temperature of 90 degrees C (recommended for virus inactivation when maintained for 90 s) was reached after boiling for 170 s, with all 50 mussels open at 210 s. For steaming, the mean internal temperature achieved was only 83 degrees C after 300 s, and all 50 mussels were open. When mussels were steamed for 180 s (mean internal temperature of 63 degrees C), a significant 1.5-log decrease in the HAV titer (log TCID50) was observed. Following the immersion of mussels in boiling water for 180 s (mean internal temperature of 92 degrees C), no viable HAV was detected. For both boiling and steaming experiments, there was no significant change in the norovirus or HAV qRT-PCR titers compared with the controls. Our results show that when New Zealand Greenshell mussels open on heating, their internal temperature may not reach the parameters required for virus inactivation. Immersion for a minimum of 3 min in boiling water rather than steaming is recommended to reduce the risk of viral foodborne illness from contaminated shellfish.

Cost-effectiveness of universal childhood hepatitis A vaccination in Chile

Hepatitis A is an important public health problem in Chile. Childhood vaccination has reduced hepatitis A rates in several countries, prompting this evaluation of its cost-effectiveness in Chile. Using a Markov model, we project mass vaccination would reduce hepatitis A cases among birth cohort members and their personal contacts >80%. Vaccination costs of US dollars 5.3-6.4 million would be offset by US dollars 9.2-9.4 million reductions in disease costs. Further, approximately 70 fatal infections would be averted and >4600 quality-adjusted life years would be saved. This analysis supports the cost-effectiveness of universal childhood hepatitis A vaccination in Chile.

High-pressure inactivation of hepatitis A virus within oysters

Previous results demonstrated that hepatitis A virus (HAV) could be inactivated by high hydrostatic pressure (HHP) (D. H. Kingsley, D. Hoover, E. Papafragkou, and G. P. Richards, J. Food Prot. 65:1605-1609, 2002); however, direct evaluation of HAV inactivation within contaminated oysters was not performed. In this study, we report confirmation that HAV within contaminated shellfish is inactivated by HHP. Shellfish were initially contaminated with HAV by using a flowthrough system. PFU reductions of >1, >2, and >3 log(10) were observed for 1-min treatments at 350, 375, and 400 megapascals, respectively, within a temperature range of 8.7 to 10.3 degrees C. Bioconcentration of nearly 6 log(10) PFU of HAV per oyster was achieved under simulated natural conditions. These results suggest that HHP treatment of raw shellfish will be a viable strategy for the reduction of infectious HAV.

Modelling effect of physical and chemical parameters on heat inactivation kinetics of hepatitis A virus in a fruit model system

While thermal destruction of pathogenic bacteria has been thoroughly studied in food industry, heat inactivation of viruses in food has been poorly investigated. Experiments were carried out to characterize the effects of controlled physical and chemical characteristics of a food matrix upon heat resistance parameters (D and z values) of hepatitis A virus (HAV), taken as model because of its reported heat resistance. Sucrose content (28-52 degrees Brix), calcium concentration (90-1700 mg kg(-1)) and pH (3.3-4.3) were selected for possible influence on thermal inactivation of HAV in strawberry mashes and thus included in an experimental design according to a Doehlert matrix. Use of this design not only allowed to detect and quantify the direct influence of sucrose concentration upon the D85 degrees C value to be higher than the one of pH, but also to reveal a sucrose concentration/pH specific interaction, while no effect of calcium concentration was evidenced. Although the model cannot be directly used to predict heat resistance in real fruit systems, because of differences observed between predicted and measured D85 degrees C values, it is useful for predicting the trends and relative changes in D values due to sucrose concentration and pH variations. Results suggested possible effects of other constituents of strawberry products on heat resistance of HAV and confirmed the importance of experimental validation of any model-derived process. Nevertheless, such a modelling approach using response surface methodology provides a rapid answer to heat resistance evaluation of a food-borne virus as a function of specific physical and chemical parameters of specific food products.

Survival and persistence of norovirus, hepatitis A virus, and feline calicivirus in marinated mussels

Noroviruses (NV) and hepatitis A virus (HAV) are foodborne enteric viruses associated with outbreaks of disease following consumption of raw or lightly cooked bivalve shellfish. Marinated mussels are a popular delicacy, but there is no published information on whether enteric viruses survive the marination process. The survival and persistence of HAV, NV, and a surrogate calicivirus, feline calicivirus (FCV), in marinated mussels over time was determined. NV, HAV, and FCV were inoculated into marinated mussels and marinade liquid and then held at 4 degrees C for up to 4 weeks. Survival of HAV and FCV was quantified by determining the 50% tissue culture infectious dose (TCID50), and these results were correlated with those of the reverse transcription (RT)-PCR assay. The persistence of nonculturable NV was determined by RT-PCR assay only. Over 4 weeks, HAV survived exposure to acid marinade at pH 3.75. There was a 1.7-log reduction in HAV TCID50 titer but no reduction in NV or HAV RT-PCR titer after 4 weeks in marinated mussels. FCV was inactivated in acid conditions although it was still detectable by RT-PCR. To simulate preharvest virus contamination and commercial marination processing, experiments using fresh mussels infected with HAV and NV were performed. HAV and NV persistence was determined using semiquantitative real-time RT-PCR, and HAV infectivity was determined by the TCID50 assay. HAV retained infectivity following simulated commercial marination and exposure to acid conditions over 4 weeks. The survival of pathogenic enteric viruses in marinated mussels constitutes a potential health risk and so is of concern to public health authorities.

Comparison of two methods for the detection of hepatitis A virus in clam samples (Tapes spp.) by reverse transcription-nested PCR

The detection of hepatitis A virus in shellfish by reverse transcription-nested polymerase chain reaction (RT-nested PCR) is hampered mainly by low levels of virus contamination and PCR inhibitors in shellfish. In this study, we focused on getting a rapid and sensitive processing procedure for the detection of HAV by RT-nested PCR in clam samples (Tapes spp.). Two previously developed processing methods for virus concentration in shellfish have been improved upon and compared. The first method involves acid adsorption, elution, polyethylene glycol (PEG) precipitation, chloroform extraction and PEG precipitation. The second method is based on elution with a glycine buffer at pH 10, chloroform extraction and concentration by ultracentrifugation. Final clam concentrates were processed by RNA extraction or immunomagnetic capture of viruses (IMC) before the RT-nested PCR reaction. Both methods of sample processing combined with the RNA extraction from the concentrates were very efficient when they were assayed in seeded and naturally contaminated samples. The results show that the first method was more effective in removal inhibitors and the second was simpler and faster. The IMC of HAV from clam concentrates processed by method 1 was revealed to be a very effective method of simultaneously removing residual PCR inhibitors and of concentrating the virus.

Foodborne viruses: an emerging problem

Several groups of viruses may infect persons after ingestion and then are shed via stool. Of these, the norovirus (NoV) and hepatitis A virus (HAV) are currently recognised as the most important human foodborne pathogens with regard to the number of outbreaks and people affected in the Western world. NoV and HAV are highly infectious and may lead to widespread outbreaks. The clinical manifestation of NoV infection, however, is relatively mild. Asymptomatic infections are common and may contribute to the spread of the infection. Introduction of NoV in a community or population (a seeding event) may be followed by additional spread because of the highly infectious nature of NoV, resulting in a great number of secondary infections (50% of contacts). Hepatitis A is an increasing problem because of the decrease in immunity of populations in countries with high standards of hygiene. Molecular-based methods can detect viruses in shellfish but are not yet available for other foods. The applicability of the methods currently available for monitoring foods for viral contamination is unknown. No consistent correlation has been found between the presence of indicator microorganisms (i.e. bacteriophages, E. coli) and viruses. NoV and HAV are highly infectious and exhibit variable levels of resistance to heat and disinfection agents. However, they are both inactivated at 100 degrees C. No validated model virus or model system is available for studies of inactivation of NoV, although investigations could make use of structurally similar viruses (i.e. canine and feline caliciviruses). In the absence of a model virus or model system, food safety guidelines need to be based on studies that have been performed with the most resistant enteric RNA viruses (i.e. HAV, for which a model system does exist) and also with bacteriophages (for water). Most documented foodborne viral outbreaks can be traced to food that has been manually handled by an infected foodhandler, rather than to industrially processed foods. The viral contamination of food can occur anywhere in the process from farm to fork, but most foodborne viral infections can be traced back to infected persons who handle food that is not heated or otherwise treated afterwards. Therefore, emphasis should be on stringent personal hygiene during preparation. If viruses are present in food preprocessing, residual viral infectivity may be present after some industrial processes. Therefore, it is key that sufficient attention be given to good agriculture practice (GAP) and good manufacturing practice (GMP) to avoid introduction of viruses onto the raw material and into the food-manufacturing environment, and to HACCP to assure adequate management of (control over) viruses present during the manufacturing process. If viruses are present in foods after processing, they remain infectious in most circumstances and in most foods for several days or weeks, especially if kept cooled (at 4 degrees C). Therefore, emphasis should be on stringent personal hygiene during preparation. For the control of foodborne viral infections, it is necessary to: Heighten awareness about the presence and spread of these viruses by foodhandlers; Optimise and standardise methods for the detection of foodborne viruses; Develop laboratory-based surveillance to detect large, common-source outbreaks at an early stage; and Emphasise consideration of viruses in setting up food safety quality control and management systems (GHP, GMP, HACCP).

Hepatitis A Transmitted by Food

Hepatitis A is caused by hepatitis A virus (HAV). Transmission occurs by the fecal-oral route, either by direct contact with an HAV-infected person or by ingestion of HAV-contaminated food or water. Foodborne or waterborne hepatitis A outbreaks are relatively uncommon in the United States. However, food handlers with hepatitis A are frequently identified, and evaluation of the need for immunoprophylaxis and implementation of control measures are a considerable burden on public health resources. In addition, HAV-contaminated food may be the source of hepatitis A for an unknown proportion of persons whose source of infection is not identified.

Detection of hepatitis A virus in shellfish (Mytilus galloprovincialis) with RT-PCR

A PCR assay for the detection of hepatitis A virus (HAV) in shellfish is described. The procedure involves the concentration of viral particles with the use of polyethylene glycol (PEG), followed by viral RNA extraction and purification with oligo(dT) cellulose. Reverse transcriptase-PCR detection was accomplished in a single step with the use of primers specific for the VP3-VP1 region of the genome. The procedure detected one 50% tissue culture infective dose (0.6 PFU) per 25 g of shellfish homogenate. Heminested PCR was then carried out to verify the specificity of the PCR products. The method was used to detect HAV in shellfish samples from EU categories B and C and to evaluate the quality of shellfish in routine monitoring for HAV in view of the relevant public health implications of this foodborne disease.

Capsid functions of inactivated human picornaviruses and feline calicivirus

The exceptional stability of enteric viruses probably resides in their capsids. The capsid functions of inactivated human picornaviruses and feline calicivirus (FCV) were determined. Viruses were inactivated by UV, hypochlorite, high temperature (72 degrees C), and physiological temperature (37 degrees C), all of which are pertinent to transmission via food and water. Poliovirus (PV) and hepatitis A virus (HAV) are transmissible via water and food, and FCV is the best available surrogate for the Norwalk-like viruses, which are leading causes of food-borne and waterborne disease in the United States. The capsids of all 37 degrees C-inactivated viruses still protected the viral RNA against RNase, even in the presence of proteinase K, which contrasted with findings with viruses inactivated at 72 degrees C. The loss of ability of the virus to attach to homologous cell receptors was universal, regardless of virus type and inactivation method, except for UV-inactivated HAV, and so virus inactivation was almost always accompanied by the loss of virus attachment. Inactivated HAV and FCV were captured by homologous antibodies. However, inactivated PV type 1 (PV-1) was not captured by homologous antibody and 37 degrees C-inactivated PV-1 was only partially captured. The epitopes on the capsids of HAV and FCV are evidently discrete from the receptor attachment sites, unlike those of PV-1. These findings indicate that the primary target of UV, hypochlorite, and 72 degrees C inactivation is the capsid and that the target of thermal inactivation (37 degrees C versus 72 degrees C) is temperature dependent.

Risk of hepatitis A infection following travel

Travel to endemic areas is one of the most frequently reported risk factors for infection with the hepatitis A virus (HAV). We evaluated the association between HAV infection and travel, by area of destination. We conducted a case-control study on all cases of HAV infection reported to the Italian National Surveillance System for Acute Viral Hepatitis in the period 1996-2000. The study population consisted of 9695 persons with HAV infection (cases) and 2590 with HBV infection (controls). The risk of acquiring HAV was highest for travel to Asia, Africa and Latin America [Odds Ratio = 9.30 (95%CI = 6.71-12.9)]; a three-fold statistically significant excess of risk was found for travel to southern Italy (OR = 3.03) and to the Mediterranean Area and Eastern Europe (OR = 3.15). Travel was implicated in 28% of the cases of HAV infection. When stratifying the analysis by area of residence (northern and central Italy vs southern Italy and the Islands), the above-mentioned risks were confirmed only for those residing in northern and central Italy, with no significant risk for those residing in southern Italy and the Islands. Travel to areas endemic for HAV infection constitutes a considerable risk. Our results highlight the importance of developing health policies for improving environmental and hygienic conditions, as well as the prevention of certain eating habits. Vaccination before travelling to a medium or high endemic area could be a safe and effective means of preventing travel-related HAV infection.

Detection of hepatitis A virus in mussels from different sources marketed in Puglia region (South Italy)

Hepatitis A virus (HAV) infection is endemic in Puglia (South Italy). Epidemiological studies indicate that shellfish consumption, particularly mussels, is a major risk factor for HAV infection, since these products are eaten raw or slightly cooked. Nested reverse transcriptase-polymerase chain reaction (RT-PCR) has been shown to be a sensitive technique for the detection of HAV in mussels. The aim of the present study was to detect the presence of HAV in a large sample of mussels by nested RT-PCR and to confirm the presence of infectious viral particles in positive samples by cell culture infection and RT-PCR confirmation. Two hundred and ninety samples of mussels from different sources were collected between December 1999 and January 2000. One hundred samples were collected before being subjected to depuration, 90 after depuration, and 100 were sampled in different seafood markets. HAV-RNA was detected in 20 (20.0%) of non-depurated mussels, in 10 (11.1%) of depurated samples, and in 23 (23.0%) of samples collected in the shellfish markets, without any significant difference in the prevalence of positive samples by collection sources (chi2 = 4.79, p = 0.09). Of the 53 samples found positive by nested RT-PCR, 18 (34.0%) resulted positive by cell culture assay. No relationship between viral contamination and bacterial contamination was found (p = 0.41). This study confirms the usefulness of molecular techniques in detecting HAV in shellfish and, thus, for the screening of a large sample of naturally contaminated mussels. Improved shellfish depuration methods are needed to obtain virus-safe shellfish and reduce the risk for public human health.

Closed-circuit system for the depuration of mussels experimentally contaminated with hepatitis A virus

In Italy, the consumption of raw or slightly cooked mussels represents the most important risk factor for the transmission of hepatitis A virus (HAV). Although there exist effective methods for the bacterial depuration of contaminated mussels, these methods are poorly effective on enteric viruses. The objective of the present study was to evaluate the effectiveness of a closed-circuit depuration system that uses both ozone and UV light for disinfecting water and that allows salinity and temperature, important parameters for the metabolism of mussels (Mytilus galloprovincialis), to be maintained at constant levels. The results showed that this depuration method decreased the viral load (from 1.72 log 50% tissue culture infective dose [TCID50] ml(-1) to <1 log TCID50 ml(-1) within 24 h and from 3.82 log TCID50 ml(-1) to <1 log TCID50 ml(-1) within 48 h). However, in both cases, after 120 h of depuration, a residual amount of virus capable of replicating in cells was detected. These results show that depuration, even if performed with advanced systems, may not guarantee the absence of virus.